NATURE 



337 



THURSDAY, FEBRUARY 13, 15 



IS MARS HABITABLE? 

 is Mars Habitable ? A Critical Examination of 

 Proj. Lowell's Book, " Mars and its Canals," with 

 an Alternative Explanation. By Dr. Alfred Russel 

 Wallace, F.R.S. Pp. xii+iio. (London: Mac- 

 niillan and Co., Ltd., 1907.) Price 2s. 6a. 



IN the year 1903 Dr. \Vallace published an interest- 

 ing and fascinating volume entitled " Man's 

 Place in the Universe," a book which created quite 

 a large perturbation in the thinking world. In it 

 he marshalled together a great number of lines of 

 iistronomical research, pointed out the deductions 

 which had generally been made from them, and by 

 weaving them together in a masterly way, drew some 

 vcrv definite conclusions from them. 



These conclusions he " cl.iimcd to have shown to 

 have enormous probabilities in their favour," and two 

 of them, which need only here be mentioned, were as 

 follows : — 



(1) That no other planet in the solar system than 

 our earth is inhabited or habitable. 



(2) That the probabilities are almost as great against 

 any other sun possessing inhabited planets. 



Not onlv, then, was a wet blanket thrown over 

 many of our favourite dreams relating to the probable 

 doings of living creatures in other worlds, but quite 

 a shock w-as received when our near neighbour Mars 

 was ruled out of court ar. .1 declared to be unin- 

 habitable ! 



We had all become accustomed to regard the 

 changes of hue on the planet's surface as due to the 

 varying tints of waxing and waning vegetable growth. 

 We pictured to ourselves the great ice caps melting 

 away under the heat rays of the approaching summer 

 ■>un. The gemination of the canals and the later 

 duplication of some of them were the means of 

 making the best use of the water after its release from 

 the poles, and the oases served as distributing centres. 

 These and many other variations of absorbing in- 

 terest all tended to indicate a world of change, very 

 different from the serenity on, let us say, the moon, 

 but more approximating to those of the earth when 

 seen from afar. 



If we are to take the view of the writer of this 

 book, such changes must be looked on rather as signs 

 of death than of life, since water, he says, there is 

 none. 



During the last decade or more the planet Mars 

 has received a considerable amount of attention. By 

 the energetic, persevering, and painstaking astronomer 

 Prof. Lowell, every portion of the planet's surface has 

 been under close observation, and the surface features 

 h.ive been chronicled on nearly every occasion when 

 l.ivourable opportunities presented themselves. 



It is not too much to say that just as the name of 

 SL:hin|)arelli is now, and will always be, identified with 

 the planet .Mars, so will that of Lowell be handed 

 down to posterity for his magnificent consecutive 

 series of observations. 



In the year 1905 Prof. Lowell published a very 

 NO 1998, VOL. 77] 



valuable volume describing in great detail, and 

 copiously illustrated with sketches and charts, the 

 observations made by him at the oppositions of 1S94, 

 1896, 1898, 1901, and 1903. 



In igo6 he published a volume which was intention- 

 ally devoid of technicalities. This was meant to con- 

 tain a summary of the main results, derived from the 

 discussion of all the data, and his own deductions as 

 to the probable cause or causes of the surface features 

 and their changes. He was led finally to make the 

 following statement with regard to the habitability 

 of Mars : — " That Mars is inhabited by beings of some 

 sort or other we may consider as certain as it is 

 uncertain what those beings may be." 



This very definite statement, made after the issue of 

 Dr. Wallace's book to which reference above has 

 been made, has called into being the present small 

 volume by the same author. Although, as we read in 

 the preface, it was commenced as a review article on 

 Prof. Lowell's recent book, it became so extended 

 that it was considered expedient to publish a more de- 

 tailed examination of the various physical problems 

 involved in order to give a complete presentation of 

 the opposite view held by Prof. Lowell. 



In directing attention to the contents of this book 

 it is not proposed to enter igto each point of the 

 arguments dealt with, but it will be sufficient to refer 

 briefly to some of them. 



The first two chapters arc devoted to a general 

 survey of the observations of Mars made by early 

 workers, concluding with those made by Prof. Lowell. 

 With regard to the last-mentioned, the author pays a 

 high tribute to the technical skill and persevering 

 labour of Prof. Low,'ell, and, while accepting all his 

 observations as valid, only parts company whh him 

 " as regards the startling theory of artificial produc- 

 tion which he thinks alone adequate to explain 

 them." 



The two main topics dealt with in chapter iii. are 

 the questions of the elaborate system of the canals 

 and the water supply. The author takes the view 

 that if the surface of the planet is so wonderfully 

 smooth and level as Prof. Lowell states it to be, then 

 the great network of straight canals could possibly 

 have been constructed by intelligent beings for irriga- 

 tion purposes. But he points out emphatically here 

 that, if it were so smooth, then such a system would 

 be quite unnecessary, as the water would naturally 

 irrigate as much of the surface as it could reach. 

 If it be admitted for a moment that the polar caps 

 are frozen water, he joins with the late Miss Gierke 

 in the view that the excessively scanty supply of 

 water, coupled w-ith the loss through evaporation, could 

 not possibly serve the innumerable canals. 



As the habitability of Mars depends on the presence 

 of water, the question of the evidence for the presence 

 or absence of water vapour is dealt with in chapter iv. 

 Dr. Wallace first directs attention to the observation of 

 the melting polar caps, and the deduction made by 

 Prof. Lowell that Ihis melting and re-forming affirm 

 the presence of water vapour in the atmosphere. It 

 will be remembered that Prof. Lowell observed blue 

 borders on the edges of the polar caps as they melted, 







